Did a Nuclear Blast Give Birth to the Moon?

Looking at the silvery Moon hanging in the sky, it's hard to believe that quiet, comforting night light was formed in an episode of incredible violence several billion years ago.

But that's exactly what scientists are proposing in a new theory about Luna's formation: they think a massive nuclear explosion occurred at the edge of Earth's core, flinging red-hot, liquid rock into space. The orbiting detritus gradually congealed into what is now our planet's lone satellite.

If this holds any water, it's bound to be controversial. Most scientists believe that the Moon formed from the debris left over when a Mars-sized object hit our newly-formed planet around 4.5 billion years ago. This is based on several modeling studies that provide a pile of evidence in favor of the idea.

There are some holes, though. For one, the Moon's chemistry is very similar to Earth's. That makes sense until you consider that in a titanic impact like the one proposed, a good portion of the offending object would be melted, vaporized, and incorporated into the wreckage that eventually formed the Moon.

But if there was no impact, there's still the matter of the explosion — how do you get a nuclear bomb to go off in the middle of the planet?

Well, the researchers think that as the molten Earth spun, radioactive thorium and uranium accumulated at the boundary between the core and mantle in large enough quantities to spark a runaway fission reaction. Heat and energy built up until Whamo! A nuclear jet pushed giant globs of molten rock into space.

Sound like a crazy idea? It is, but the scientists think there's a way to test the idea: look for isotopic signatures on the Moon left over from when the "georeactor" exploded. If they're there, it's a good chance that Earth once went critical in a huge way, and our ghostly galleon was tossed into the heavens by the world's first nuclear detonation.